1. Field of the Invention
The present invention relates to a metal oxide-containing film-forming composition for forming a metal oxide-containing film to be used in a multi-layer resist process used for fine processing in a manufacturing process of semiconductor devices and the like; a metal oxide-containing film-formed substrate; and a patterning process using the composition.
2. Description of the Related Art
With highly integrated LSI's providing highly increased speeds, finer pattern rules are being rapidly promoted. Commensurately with the fineness, the lithography technique has attained formation of fine patterns, by virtue of light sources of shorter wavelengths and resist compositions appropriately selected therefor. The main role thereof was played by positive photoresist compositions to be each used as a monolayer. The monolayer positive photoresist composition is configured to possess, in a resist resin, a frame having an etching resistance against dry etching by chlorine-based or fluorine-based gas plasma, and to possess such a resist mechanism that an exposed portion is made dissolvable, so that the exposed portion is dissolved to thereby form a pattern, and the remaining resist pattern is used as an etching mask to dry etch a processing substrate coated with the resist composition.
However, when a pattern is made finer, i.e., pattern rules are further narrowed while keeping a thickness of a used photoresist film as it is, the photoresist film is deteriorated in resolution performance. Further, when the resist film is to be developed by a developer to form a pattern, a so-called aspect ratio thereof is made excessively large, thereby resultingly causing a pattern collapse. Thus, the fineness has been accompanied by decrease in photoresist film thickness.
Meanwhile, although for processing of a processing substrate, there is typically used a method for processing the processing substrate by dry etching by adopting a patterned photoresist film as an etching mask, practically no dry etching methods exist to exhibit a complete etching selectivity between a photoresist film and a processing substrate, so that the resist film is also damaged during processing of the processing substrate and the resist film is collapsed, thereby failing to accurately transfer a resist pattern onto the processing substrate. Thus, with finer patterns, resist compositions have been required to have higher dry etching resistances.
Further, since shortened wavelengths of exposure have demanded that resins having lower light absorption at exposure wavelengths are used for resist compositions, such resins have been subjected to a transitional history from a novolak resin, through polyhydroxystyrene, and to a resin having an aliphatic polycyclic frame, commensurately with a transitional history from i-beam, through KrF, and to ArF. However, etching speeds under the dry etching condition have been practically made higher, so that recent photoresist compositions having higher resolutions practically tend to be rather lowered in etching resistance.
This obliges a processing substrate to be dry etched by a photoresist film which is inevitably thinner and weaker in etching resistance, thereby making it urgent to ensure a material and a process in this processing state.
As one method to solve such a problem, multi-layer resist process have been used. The methods are configured to: interpose a resist intermediate film having an etching selectivity different from that of a photoresist film, i.e., a resist upper layer film, between the resist upper layer film and a processing substrate; obtain a pattern in the resist upper layer film; thereafter transfer the pattern to the resist intermediate film by dry etching by using the obtained resist upper layer film pattern as a dry etching mask; and further transfer the pattern onto the processing substrate by dry etching by using the obtained pattern of the intermediate film as a dry etching mask.
In a bilayer resist process as one of the multi-layer resist processes, a silicon-containing resin is used as a resist composition of a upper layer film, and a novolak resin is used as an intermediate film (Japanese Patent Laid-Open (kokai) No. H6-95385, for example). The silicon resin exhibits an excellent etching resistance against reactive dry etching by oxygen plasma, but is easily etched and removed by using fluorine-based gas plasma. In turn, the novolak resin is easily etched and removed by reactive dry etching by oxygen gas plasma, but exhibits an excellent etching resistance against dry etching by fluorine-based gas plasma, chlorine-based gas plasma, or the like. Thus, a novolak resin film as a resist intermediate film is formed on a processing substrate, and a resist upper layer film adopting a silicon-containing resin is formed thereon. Next, the silicon-containing resist film is subjected to pattern formation by a post treatment such as irradiation of energy beam, development, and the like, and the formed pattern is used as a dry etching mask in a manner to remove a novolak resin by reactive dry etching based on oxygen plasma at those portions of the novolak resin where the resist pattern material has been developedly removed, to thereby transfer the pattern to the novolak film. Further, the pattern transferred to the novolak film is used as a dry etching mask, thereby enabling pattern transference to the processing substrate by etching based on fluorine-based gas plasma, chlorine-based gas plasma, or the like.
Since such a pattern transference based on dry etching leads to obtainment of a transferred pattern in a relatively excellent profile when an etching resistance of the etching mask is sufficient, problems are scarcely caused such as pattern collapse due to friction or the like by a developer upon development of a resist, thereby allowing for obtainment of a pattern having a relatively large aspect ratio. Thus, even for a fine pattern which has not been directly formed due to pattern collapse upon development or the like due to a problem of aspect ratio when a resist film exemplarily adopting a novolak resin has been made to have a thickness corresponding to that of the aforementioned intermediate film, the above-described bilayer resist process allows for obtainment of such a novolak resin pattern having a sufficient thickness as a dry etching mask of a processing substrate.
The multi-layer resist process further include a three-layer resist process which can be performed by using a typical resist composition used in a monolayered resist process. For example, this method is configured to form: an organic film as a resist lower layer film based on novolak or the like on a processing substrate; a silicon-containing film as a resist intermediate film, thereon; and a typical organic photoresist film as a resist upper layer film, thereon. Since the organic resist upper layer film exhibits an excellent etching selectivity ratio relative to the silicon-containing resist intermediate film for dry etching by fluorine-based gas plasma, the resist pattern is transferred to the silicon-containing resist intermediate film by means of dry etching based on fluorine-based gas plasma. According to this method, patterns of novolak films having sufficient dry etching resistances for processing can be obtained similarly to the bilayer resist process insofar as patterns can be transferred to silicon-containing films, even by adopting: a resist composition which is difficult to be formed with a pattern having a sufficient film thickness for direct processing of a processing substrate; and a resist composition having an insufficient dry etching resistance for processing of a substrate.
Examples of silicon-containing resist intermediate films to be used in the above-described three-layer resist process include silicon-containing inorganic films by CVD, such as SiO2 films (Japanese Patent Laid-Open (kokai) No. H7-183194, for example) and SiON films (Japanese Patent Laid-Open (kokai) No. H7-181688, for example); and films obtained by spin coating, such as SOG (spin-on-glass) films (Japanese Patent Laid-Open (kokai) No. H5-291208, J. Appl. Polym. Sci., Vol. 88, 636-640 (2003), for example), and crosslinkable silsesquioxane films (Japanese translation of PCT international application No. 2005-520354, for example); and polysilane films (Japanese Patent Laid-Open (kokai) No. H11-60735, for example) would also be usable. Although the SiO2 films and SiON films have excellent performances as a dry etching mask upon dry etching of an underlying organic film, a specific equipment is required for film-formation. Contrary, the SOG films, crosslinkable silsesquioxane films, and polysilane films can be formed by only spin coating and heating, and are thus considered to be high in process efficiency.
The applicability of the multi-layer resist process is not restricted to an attempt to enhance a resolution limit of resist film. In a via-first method which is one of substrate processing methods where a processing intermediate substrate has large height differences, an attempt to form a pattern with a single resist film encounters a problem such as inaccurate focusing during resist exposure due to a substantial difference in resist film thickness. In such a case, the height differences are filled by a sacrificial film and flattened thereby, then a resist film is formed thereon and a resist pattern is formed, and this situation inevitably entails usage of the aforementioned multi-layer resist process (Japanese Patent Laid-Open (kokai) No. 2004-349572, for example).
Silicon-containing films having been conventionally used in such a multi-layer resist process have several problems. For example, it is well known that when a resist pattern is intended be formed by photolithography, exposure light is reflected by a substrate and interferes with incident light, to cause a problem of so-called standing waves, and it is required to interposingly provide an antireflective film as an intermediate film so as to obtain a fine pattern which is free of edge roughness of photoresist film. Particularly, reflection control is indispensable, under the most-advanced high NA exposure conditions.
Then, it becomes necessary to interpose an organic antireflective film between a silicon-containing film and a photoresist film to be formed on the silicon-containing film, in a process for forming the silicon-containing film as a resist intermediate film, particularly by CVD in a multi-layer resist process. However, when such an organic antireflective film is to be additionally interposed, it becomes necessary to pattern the organic antireflective film by using the photoresist film as a dry etching mask, such that transference to processing of the silicon-containing film is allowed after dry etching of the organic antireflective film by using the photoresist film as the mask upon dry etching. As such, the overlying photoresist film is subjected to an additional burden of dry etching to an extent the processing of the organic antireflective film. Particularly, most-advanced photoresist films have been made small in thickness, so that such dry etching burden is not negligible. Thus, attention has been directed to a three-layer resist process utilizing a light-absorbing silicon-containing film as a resist intermediate film which is free of occurrence of the aforementioned etching burden.
Known as such a light-absorbing silicon-containing film to be utilized as a resist intermediate film, is a spin coating type of light-absorbing silicon-containing film. Exemplarily disclosed is a technique for causing the film to have an aromatic structure as a light-absorbing structure (Japanese Patent Laid-Open (kokai) No. 2005-15779).
However, since the aromatic ring structure for effective light absorption has a function to lower a dry etching speed in case of dry etching by fluorine-based gas plasma, this is a disadvantageous way to conduct dry etching of a resist intermediate film without burdening a photoresist film. Then, since addition of a large amount of such light-absorbing substitutional groups is undesirable, it is required to restrict the addition amount to a minimum.
Further, the dry etching speed for reactive dry etching by typically used oxygen gas plasma upon processing of a resist lower layer film while using a resist intermediate film as a dry etching mask, is to be preferably low so as to increase an etching selectivity ratio between the resist intermediate film and the resist lower layer film, so that such a resist intermediate film is desired which has a possibly higher silicon content exhibiting a higher reactivity with a fluorine-based etching gas so as to obtain such a dry etching characteristic. As noted above, those films are preferable having higher contents of silicon which is a component having a higher reactivity with a fluorine gas, in view of the requirement from the processing conditions of both the overlying photoresist film and the underlying organic film.
Actual silicon-containing intermediate film-forming compositions of spin coating type contain organic substitutional groups so that a silicon-containing compound is made dissolvable in an organic solvent. There is disclosed a composition for forming a SOG film among known silicon-containing films as resist intermediate films in lithography using KrF excimer laser light in the J. Appl. Polym. Sci., Vol. 88, 636-640 (2003).
However, since no descriptions are found concerning a light-absorbing group for the disclosed composition, it is supposed that a silicon-containing film to be obtained from the composition fails to have an antireflective function.
This fails to prevent reflection upon exposure in lithography using a most-advanced high-NA exposure system, thereby possibly failing to obtain a finer resist pattern profile.
Moreover, since photoresist films have been further decreased in thickness in a most-advanced semiconductor process using the above-described high-NA exposure system, it is predicted that a pattern transference to a silicon-containing intermediate film is made difficult in case of etching the intermediate film by using a photoresist film as an etching mask, when a silicon content of the silicon-containing intermediate film is merely increased while possessing an antireflective function. As such, materials having faster etching speeds are expected.
As described above, resist intermediate films to be used in multi-layer resist process are required to realize: excellent dry etching characteristics relative to resist upper layer films and resist lower layer films; and highly fine resist pattern profile.
Particular concern in a composition for forming a resist intermediate film having a higher silicon content rate, is a storage stability of the composition. Silanol groups present in silicon-containing compounds included in the compositions sometimes condense, so that molecular weights of silicon-containing film-forming compositions are changed.
Typically, when a hydrolyzable silicon compound is affected by water in the presence of an acid catalyst, a hydrolyzable substitutional group(s) is/are subjected to hydrolysis, to form a silanol group(s). The silanol group is further subjected to a condensation reaction with another silanol group or an unreacted hydrolyzable group, to form a siloxane bond. This reaction is successively and repetitively caused, to resultingly form a silicon-containing compound, so-called an oligomer, polymer, or a sol as the case may be. At this time, the condensation reaction is progressed sequentially from the silanol group having the highest reactivity among those silanol groups derived from monomers, oligomers, polymers, and the like produced by hydrolysis reaction in the system, in a manner to consume silanol groups belonging to the monomers, oligomers, polymers, and the like, thereby forming a silicon-containing compound. Moreover, such a condensation reaction occasionally progresses endlessly, to an extent that the silicon-containing compound solution is eventually gelated. In such a condition, film thickness fluctuation, lithography performance fluctuation, and the like are observed. Since fluctuation of lithography performance is particularly delicate, such a fluctuation is inevitably observed as a change of finer pattern profile even when condensation of silanol groups in molecules is not observable as a film thickness increase or a molecular weight change.
It has been conventionally described that such a highly reactivity silanol group can be relatively stabilized when the same is preserved in an acidic state, in a C. J. Brinker and G. W. Scherer, “Sol-Gel Science: The Physics and Chemistry of Sol-Gel Processing”, Academic Press, San Diego, p. 120 (1990) and the like.
Further, there has been disclosed addition of water so as to improve a storage stability, in the J. Appl. Polym. Sci., Vol. 88, 636-640 (2003), Japanese Patent Laid-Open (kokai) No. 2004-157469, Japanese Patent Laid-Open (kokai) No. 2004-191386, and the like.
However, even when such countermeasures are taken for silicon-containing compounds in silicon-containing film-forming compositions produced in the above methods, it is actually impossible to completely stop condensation reactions of silanol groups, so that the silicon-containing compounds slowly change over time, and natures of silicon-containing films to be obtained from the thus changed silicon-containing film-forming compositions are also changed. As such, it has been necessary to preserve them by refrigerating or freezing until just before usage thereof, and to bring them back to a service temperature (typically 23° C.) upon usage in a manner to swiftly use them up.
Meanwhile, in an actual manufacturing process of a semiconductor device, defects are occasionally caused in coated films formed on the substrate, and re-processing is thus to be performed. Conventional SOG films have compositions substantially equivalent to SiO2. Thus, to remove the films, dry delamination or the like based on hydrofluoric acid or fluorine gas has been conducted, but such a removal technique has brought about a serious damage against the substrate.
Against such a problem, there has been sought for a silicon-containing film-forming composition which can be subjected to wet delamination for utilizing a sulfuric acid-hydrogen peroxide-water mixture or ammonia-hydrogen peroxide-water mixture typically used in a conventional semiconductor device production process.